The invention relates to an electric fish scaring or repelling device, intended particularly for water inlet and extraction structures, in which several main electrodes are positioned below the surface of the water and connected to a voltage supply unit which produces a pulsed voltage pattern.
Fish-scaring devices are used as a measure to conserve fish stocks and to avoid interruptions in the operation of and the risk of damage to items of equipment in power stations. These devices are installed in the vicinity of water inlet and extraction structures and prevent corresponding damage to the environment as a result of the destruction of organisms living in the water, particularly fish. Electric fish-scaring devices already in use contain a number of main and counter-electrodes which are positioned at appropriate intervals, and which are connected to the terminals of a d.c. or a.c. voltage supply unit. This voltage supply unit generates series of positive and negative pulses which are supplied to the main and counter-electrodes. Known fish scaring devices of the type described above are kept in operation with practically no further checks after preliminary tests and the comprehensive measurements and adjustments of the device carried out during commissioning. As a result a change and particularly a reduction in the scaring effect are noticed only when considerable damage has occurred.
Such changes in the scaring effect can occur as a result of fluctuations in the electrode characteristics, which may, for example, take the form of an accelerating increase in the surface resistance or of changing characteristic values of water composition, particularly the conductivity of the water, which determines the extent of the field, and the distribution of the organisms.